Tool and Method to Plug and Abandon Well

ABSTRACT

A tool ( 10 ) is described for the handling of wells through a formation, and which shall be taken out of operation with a device for a closing plug of a material that can be hardened, such as concrete, where there is a casing pipe in the well that is cemented against the wall in the bore hole with concrete, and it is characterised in that the tool comprises an assembled unit ( 10 ) from the following three sections; a perforating lance ( 32 ) comprising a number of explosive charges to form by detonation a row of holes in the pipe and out into the surrounding layer of concrete, a cleaning unit ( 34 ) for mechanical cleaning of the inner wall of the pipe in the perforated area and a flushing unit ( 36 ) to loosen, dissolve and flush away the hardened cement material between the outer wall of the pipe and the wall of the bore hole. Also described is a method to plug a well that shall be taken out of operation.

The present invention relates to a tool for handling of wells through a formation, and which shall be taken out of operation by installing a closing plug of a hardenable material, such as concrete, where there is a casing pipe in the well which is cemented towards the wall of the bore hole with a concrete, as defined in the introduction of claim 1.

The invention also relates to a special construction of a perforating gun to provide perforations in a pipe in a formation and comprising an extended lance fitted with a number of explosive charges around the circumference and along the length of the lance, and also means for the detonation of the explosive charges.

Furthermore, the invention relates to a method as described in the introduction of claim 12 for the closing off of a well including a casing pipe through a formation in that a plug of a hardenable material is established, whereby a section of the casing pipe through the well is perforated and a material that can be hardened is conducted down through the pipe and is brought to flow out through the perforations and make contact with the walls of the original bore hole.

The invention concerns a tool that is used in connection with the plugging of wells that shall be taken out of operation.

When production of hydrocarbons from a porous HC containing field in the rock formation is established, a well bore is drilled down into the formation, and a casing pipe (production pipe) is set down into the well bore and is secured and stabilised in relation to the walls of the original bore hole in that concrete is sprayed in between the outer wall of the pipe and the wall of the bore hole.

When such a production well shall be taken out of production it is completely plugged with a concrete plug so that one does not risk future leakages. The plugging of such a well involves the pumping in of a plugging material from a hardenable concrete. The requirement of such a plug is that the concrete being pumped down shall make direct contact with the porous formation.

Therefore, it is common that the production pipe (the casing pipe) is perforated, the pipe is cleaned internally and an acidic cleaning fluid is sprayed in to dissolve the concrete.

This three part operation is carried out in that a perforating tool which is fitted with a number of directed explosive charges is lowered down. When these are fired, a set of holes is blasted into the pipe to wash out and partially dissolve the original concrete so that the new and fresh concrete can make a proper direct contact with the rock formation while establishing the plug.

After the perforating gun has been fired it is common to clean the pipe internally by lowering down a cleaning tool that grinds off protruding bits of metal and fibres from the pipe inside, and which are formed as a consequence of the explosion.

The cleaning tool can be a brush that brushes, rubs or grinds the pipe internally.

When the pipe is ground and cleaned, a flushing tool is lowered down with an upper and a lower set of gaskets that seal against the inner wall of the pipe. A cleaning fluid is sprayed out between these sets of gaskets, usually containing an acid that can flush loose bits of concrete or possibly directly dissolve the concrete chemically. These bits of concrete and concrete remains is then flushed with the flow of fluid upwards in through the annular space between the pipe in which the tool is suspended from the surface and the inside of the casing pipe.

With regard to prior art, reference is made to US-2002/162657, US-2007/163783, U.S. Pat. No. 5,372,198, US-2010/236781, U.S. Pat. No. 6,347,673 and US-2006/196693. For example, it can be seen in FIG. 4 of said US-2002/162657 that the lance can perforate the pipe and plug the well with concrete in a combined operation.

It is an aim of this invention to further develop the known solutions so that all these three operations can be combined into one and the same apparatus, i.e. without the operating line or the pipe having to be pulled up to the surface to change a tool a number of times for each operation where a well shall be plugged.

It is a further aim to provide a new construction of a perforating un to be able to improve the cleaning of the concrete from the annular space between the casing pipe and the wall of the bore hole.

The tool according to the invention is characterised in that it comprises an assembled unit of the following three sections: a perforating lance comprising a number of explosive charges which, by detonation, form a row of holes in the pipe and out into the surrounding layer of concrete, a cleaning unit for mechanical cleaning of the inner wall of the pipe at the perforated area and a flushing unit to loosen, dissolve and flush away the hardened cement material between the outer wall of the pipe and the wall of the bore hole.

The unit is preferably fitted to the end of the operating string or pipe that is guided down into the well from an installation at the surface.

The perforating lance is preferably arranged at the bottom of the unit, the flushing unit is fitted to the operating string, while the cleaning unit is inserted between the lance and the flushing unit.

The perforating lance is preferably set up to be released from the other parts of the unit after the explosive charges have been detonated/fired. The perforating lance has a number of charges around and along the circumference.

The explosive charges are preferably formed, in connection with the perforating lance, with different explosive strength in the different sections (A,B,C) of the lance. Alternatively, an upper (A) section of the perforating gun/-perforating lance is formed with greater explosive power in the explosive charges than the rest of the charges.

The preferred embodiments of the tool according to the invention are characterised by the features that are given in claims 1-11.

The method according to the invention is characterised in that a three-part tool is used, encompassing a lower part comprising a perforating gun (32) to establish said perforations, a middle cleaning part (34) to clean the pipe (20) inside and also an upper flushing section (36) with a flushing fluid to flush loose and dissolve concrete remains in the space between the pipe (20) and the wall of the bore hole The following steps are carried out in sequence:

-   a) the tool (10) connected to an operating string (30) is guided     down through the pipe until the perforating gun (32) is in a     position where the pipe shall be perforated, -   b) the explosive charges (33) are detonated to establish the     perforations (35) in the pipe, -   c) the tool (10) is conducted up and down in the perforated area to     scrub-clean the inner pipe wall with the help of the cleaning part, -   d) the tool (10) is positioned so that the flushing section (36) in     the pipe is placed adjoining a set of the perforation holes and such     that a number of perforation holes around the circumference lie     above the flushing section (36) and form a fluid connection from the     annular space between the pipe (20) and the wall of the well and     into the annular space (12) between the operating string (30), -   e) flushing liquid is pumped out through the perforations to loosen     bits of concrete and dissolve the concrete in the space outside the     pipe (20) so that this is led back through the upper perforations     and into the pipe (20) above the flushing section (36), and -   f) the tool is removed and a material that can be hardened is     lowered down to fill a given section of the pipe (20) and the     interstitial space between the outer side of the pipe and the wall     of the bore hole, whereby the well is plugged when the material     hardens.

It is preferred that a tool as described in the claims 1-11 is used.

The invention shall be explained in more detail with reference to the enclosed figures, in which:

FIG. 1 shows a tool according to the invention and how it is set up to be installed in a well and operated from a platform on the surface of the ocean.

FIGS. 2, 3 and 4 show an enlarged cross-section of the tool installed down in the well.

FIG. 5 shows an enlargement to show details of the perforating lance.

FIG. 1 shows a tool according to the invention 10 fitted to a string or pipe 30 that runs down through a formation 14 from an installation 100, a platform 100 on the ocean or the like. The ocean surface is shown by 18 and the sea bed by 16. The construction according to the invention can, of course, also be used in connection with an HC exploring installation on land.

A casing pipe (production pipe) (20) is inserted into the bore hole or the well and this is cemented with concrete 22 to the walls of the bore hole.

The tool 10 according to the invention is also shown in the figure. It is composed of the three parts, the perforating gun 32, the scrubbing/cleaning unit 34 and the flushing device 36 seen in a direction from below.

According to the invention the washing/flushing unit 36 is placed at the top of the combined unit and is connected uppermost in the tool 10 to the lower end of the pipe/line 30. Between the pipe/line 30 and the inside of the casing pipe 20, there is an annular space 12 through which loosened bits of concrete and other impurities can be led during the cleaning/flushing.

The scrubbing/cleaning unit 34 is fastened immediately below the flushing unit 36 and below this the perforating gun 32 is placed. They consequently form a three part tool with all the functions in one piece.

FIG. 2 shows an enlarged cross-section of the apparatus according to the invention.

Perforating Gun 32.

This comprises a cylinder formed column or casing that extends downwards below the scrubbing/cleaning unit and where a number of dedicated explosive charges/explosives 33 are inserted around the periphery and in several rows on the surface, in a previously known manner, i.e. that the blast from the charges are in a horizontal or an inclined direction radially outwards towards the pipe to blow holes in the pipe wall. The explosive charges are connected to a trigger unit, for example, via a primer cable which runs from the surface through the pipe 30. The charges are made to explode simultaneously and they are facing radially outwards and each one of the charges blasts a hole 35 in the metal of the casing pipe 20 so that a fluid connection is formed radially outwards to the concrete outside the pipe. The size of the individual holes can be regulated with the help of the blasting strength of the individual charges 33.

The Scrubbing/Cleaning Unit 34

This cleaning unit comprises brushes, grooves, sharp scraping edges or is grooved 37 on the radially outwardly facing head surface. The diameter of the head is adapted to the inner diameter of the pipe 20. After the detonation, metal remains with sharp edges extending in from the pipe surface around these openings are created. The brushes 37 that can comprise metal brushes such as a so-called steel brush shall loosen and remove such sharp edges. The cleaning brushes can be formed around the circumference so that they can be pulled radially inwards into the tool construction when they are not in use, and be pushed out to make contact with the inner wall of the pipe when the cleaning shall take place. A separate mechanism inside the scrubbing part, for example, hydraulically operated, can be reset to be pushed out against the wall, or be pulled in from the wall.

To adjust the tool to different inner diameters of the casing pipe 20, the brushes can be extendable and retractable in a radial direction. They scrape the inner wall only in that the whole apparatus is moved up and down as shown by the arrow P in FIG. 2.

The Washing/Flushing Unit 36

This comprises two cupola formed bellows (for example, from rubber) 36 a and 36 b which mutually are fitted a short distance apart to the tool line/pipe 30. They form a seal against the inner wall of the pipe 20. Between them they form an annular flushing unit space 38. The pipe 30 is perforated in this annular space with holes 40 for the spraying out of liquid (water-acid) to the space 38 and which is supplied with pressure from the surface through the inside of the pipe 30. A fluid pressure arises in the intermediate annular space 38 and the liquid is forced out through the perforations 35 that are blasted out and loosens and sprays bits of concrete in the annular space 22 between the casing pipe and the wall of the bore hole.

Thus, this flushing unit 36 is placed uppermost in the construction and connected to the above lying pipe and the brushing unit 34 is placed below this and the perforating gun 32 is placed underneath this again at the end of the tool.

FIG. 3 shows a first step in the process. The tool 10, with the three parts, is set up for firing the explosive charges. A blasting is carried out and holes 35 are made in the pipe. The holes 35 run out through the pipe 20 and the explosion also leads to holes being formed more or less in the concrete coat 22 radially outside and which one wants to break up and remove as much as possible.

After the blasting has been carried out the tool is led up and down so that the brushes 37 of the tool 34 can clean the internal surface of the pipe along the holes at the bottom of FIG. 3.

FIG. 4 shows an important feature of the invention. The perforating gun 32 is loosened, with the help of a release mechanism not described further, from the rest of the tool and falls down into the well. After the gun 32 has been dropped, the whole tool is lowered further down so that the flushing unit 36 is aligned with the holes 35.

Now, the spraying starts in that water/acid is pumped down through the pipe 30 shown by the arrows 42. It can be seen that the bottom of the tool, i.e. the part which lies above the perforating gun, is sealed with a plate 50 so that the cleaning fluid which is sent down under pressure is forced out into the annular space 38. The annular space 38 between the two sealing bellows 36 a, 36 b is filled with fluid and at a pressure that forces the fluid out through the holes 35 and out into the concrete part one wishes to remove. The acid in the water will contribute to dissolving the concrete chemically. Furthermore, the water pressure out through the holes will lead to parts of the concrete coat being broken up into smaller and larger pieces. It is shown with the arrows P1 how the fluid flows further upwards and radially back inwards through the holes/openings above the sealing bellows. Then, flushed out fluid can be led further upwards through the annular space 12 between the pipe 30 and the inner wall of the casing pipe.

After most of the concrete coat is removed, the construction is ready for the feeding of concrete to form a plug in the well. This concrete is filled internally in the casing pipe and will flow out through the holes and also fill up the back space between the outer wall of the casing pipe and the walls of the original bore hole.

Preferred Embodiment of the Perforating Gun/Perforating Lance

According to a preferred embodiment which is outlined in FIG. 5, the lance-formed perforating gun is fitted with sections with different strengths of explosive charges. These sections are marked A, B and C in FIG. 5. Initially, the directed charges are designed to give an optimal hole diameter in the casing pipe in the well plus some distance into the existing concrete coat which one wishes to be able to flush loose and flush away or to dissolve chemically with the acid content of the liquid.

By increasing the power of the explosive charges in the upper A and lower C sections in relation to the middle section B, the holes in A and C will have greater diameters, and thus a better and higher circulation effect and pressure profile of the flushing fluid during the circulation sequence. The counter pressure during the washing sequence will be reduced so that the pumping rate can be increased. With reference to the flow pattern shown by the arrows P1 and P2 in FIG. 4, bits of concrete that have come loose will flow upwards in the gap outside the outer wall of the pipe to flow through the upper holes and back into the annular space 12 between the pipe 12 and the inside of the casing pipe. By the holes in the upper pipe section A having a larger diameter than further down means that larger loosened bits of concrete can be cleaned out and flow through the holes at the top and thereby back into the annular space 12 to be further carried away. A perforating lance of this type can have a length of 5 to 50 meters and can be divided into the sections A,B and C as mentioned above in the context of explosive power for the individual charges.

After the charges in the perforating gun/perforating lance have been fired, it is preferred to release the lance from the rest of the tool.

A sealing plug 150, see FIG. 1, can be placed at the bottom of the pipe and form the bottom of the pipe which shall now be filled with concrete. This can take place in that the bottom of the tool is removed and the concrete is pumped in from the surface and downward through the pipe 30 to fill this and to flow into the space below and outside the tool. The concrete will flow out through the perforations 35 and partially fill the space cleaned of concrete between the outer wall of the pipe and the rock formation in the bore hole. In this way a direct concrete contact between the rock formation 14 will be formed. 

1. Tool for the handling of a well through a formation, and which shall be taken out of operation by arranging a closing plug of a material that can be hardened where there is a casing pipe in the well which is cemented with concrete against the a wall in the bore hole, characterised in that the tool comprises an assembled unit from the following three sections: a perforating lance comprising a number of explosive charges to form by detonation a perforated area in the pipe and exposed to the surrounding layer of concrete, a cleaning unit for mechanical cleaning an inner wall of the pipe at said perforated area, and a flushing unit for the spraying in of a fluid to release, dissolve and flush away hardened cement material between an outer wall of the pipe and the wall in the bore hole.
 2. Tool according to claim 1, characterised in that said perforating lance is arranged as an end piece of the said assembled unit, said flushing unit is fitted to an operating line, the and said cleaning unit is inserted between said lance and said flushing unit.
 3. Tool according to claim 1, characterised in that said perforating lance is set up to be released from the rest of said assembled unit after said explosive charges have been detonated.
 4. Tool according to claim 1, characterised in that said perforating lance has a number of said explosive charges around and along the circumference thereof.
 5. Tool according to claim 1, characterised in that said explosive charges in said perforating lance are formed with different blasting strengths in different sections of said lance.
 6. Tool according to claim 1, characterised in that an upper section of said perforating lance is formed with greater explosive power in said explosive charges than the rest of said explosive charges.
 7. Tool according to claim 1, characterised in that an upper and a lower(C) section of said the perforating lance are formed with a greater explosive power in said explosive charges than those explosive charges in a middle section.
 8. Tool according to claim 1, characterised in that a said cleaning unit comprises a scrubbing unit for mechanical cleaning of the inner wall of the pipe in said perforated area.
 9. Tool according, to claim 1, characterised in that said cleaning unit scraping edges on a radially outwardly facing head surface thereof.
 10. Tool according to claim 1, characterised in that said flushing unit is set up to spray out a fluid to loosen, dissolve and flush away the hardened mass of cement between the outer wall of the pipe and the wall of the bore hole.
 11. Tool according to claim 1, characterised in that the tool is fitted to the end of an operating line which is lowered down into the well from an installation on the surface.
 12. Method to close off a well including a casing pipe through a formation in that a plug of a material that can be hardened is established, whereby a section of the casing pipe through the well is perforated, and a hardenable material is led down through the pipe and is brought to flow out through the perforations and make contact with the walls in the original bore hole, characterised in that a three-part tool is used encompassing a lower part comprising a perforating lance gun to form said perforations, a middle cleaning part to clean the pipe internally and also an upper flushing section with a cleaning fluid to flush loose and dissolve concrete residues in the space between the pipe and the wall of the bore hole, and the following steps are carried out in sequence, a) the tool connected to an operating line is fed down through the pipe until the perforating lance is in a position where the pipe is to be perforated, b) the explosive charges are detonated to establish the perforations in the pipe, c) the tool is conducted up and down in the perforated area to scrub clean the inner wall of the pipe with the help of the cleaning part, d) the tool is positioned so that the flushing section in the pipe is placed adjoining a set of perforated holes and such that a number of perforated holes around the circumference lie above the flushing section and form a fluid connection from the annular space between the pipe and the wall of the well and into the annular space between the operating line, e) flushing fluid is sprayed out through the perforations to loosen bits of concrete and dissolve the concrete in the space outside the pipe so that this is led back through the upper perforations and into the pipe above the flushing section, and f) the tool is removed and a material that can be hardened is lowered down to fill a given section of the pipe and the gap between the outer side of the pipe and the wall of the bore hole, whereby the well is plugged when the material is hardened.
 13. (canceled)
 14. A tool for plugging a well comprising a lance having a plurality of explosive charges therein for forming a series of holes in a pipe disposed within a well bore; a cleaning unit disposed above said lance and having scraping edges on a radially outwardly facing surface thereof for scraping of an inner wall of the pipe; and a flushing unit disposed above said cleaning unit and having a pair of longitudinally spaced apart bellows for sealing against the pipe and defining a space therebetween and a plurality of holes for communicating with said space for spraying a flushing fluid into said space.
 15. A tool as set forth in claim 14 wherein said lance is removably mounted on said tool for ejection therefrom.
 16. A tool as set forth in claim 14 wherein said scraping edges of said cleaning unit are disposed circumferentially of said cleaning unit and are radially retractable. 